The most common cause of cardiovascular disease is atherosclerosis, a chronic inflammatory response in the walls of arteries due to accumulation of an atheromatous plaque at the vessel wall that leads to hardening of an artery and loss of blood flow. Often, the diseased vessels will require surgical repair, either through implantation of a stent or replacement or bypass with a synthetic or natural vascular graft.
Both of these options are problematic, however. For instance, the six month restenosis rate for a vessel following implantation of a stent is about 20% for large diameter vessels and almost 33% for small diameter vessels. When considering replacement or bypass, even when utilizing a saphenous vein autograft, the ten year patency of the graft is about 50%, and synthetic prostheses have even lower patency rates. Moreover, suitable saphenous veins are often unavailable for utilization and morbidity rates increase with this approach.
One of the primary problems with available vascular graft materials is the mismatch between mechanical properties of the native and the implanted materials. Native vessels are elastic in nature and expand under pressure during blood flow. A mismatch between the elastic characteristics of a native vessel and an implant segment can disturb the blood flow pattern due to both velocity and pressure changes as well as geometric inconsistencies. For instance, FIGS. 1A-1C schematically illustrate flow inconsistencies that can occur due to this mismatch between a native vessel and an implanted vessel segment. FIG. 1A illustrates a native vessel 10 with a regular blood flow pattern indicated by the directional arrows. In FIG. 1B, vessel 10 includes an implanted vessel segment 12 that describes greater expansion under pressure than that of the native vessel 10. As can be seen, the implanted vessel segment 12 can expand beyond the diameter of the native vessel, leading to a more turbulent flow pattern through the segment. Likewise, with reference to FIG. 1C, the addition of a vessel segment 14 that describes less expansion under pressure than a native vessel 10, can also lead to development of a more turbulent flow pattern through the vessel. Disturbed blood flow patterns due to mechanical property mismatch between native and implanted vascular tissue has been implicated in low patency rates for grafts.
What are needed in the art are synthetic materials that can be formed to more closely mimic the mechanical characteristics of native tissues to which they can be grafted.